Automotive-type alternators, particularly when combined with rectifiers, place high requirements of cooling on the rectifier elements. Additionally, the rectifiers should be protected against mechanical damage and, further, should be shielded against accidental contact by the user, or during maintenance of the alternator or the vehicle with which it is used. It has, therefore, been proposed to use cover caps with generators which are intended to separate the alternator and rectifier components which carry electrical current and which require cooling from other components of the machine, and to protect these elements against accidental contact. They must, however, be so constructed that they do not provide a complete air-tight enclosure since they must permit ingress of cooling air to the rectifier components and to the remainder of the generator. In many such known constructions, the end bell or end cover plate of the alternator itself, which is located close to the slip ring side--and remote from the drive side of the alternator--is formed with air ingress openings. The end cover plate, thus, takes over the function of an air directing and air inlet element. In some constructions, the cover plates or end bells simulaneously support the bearings and, thus, the cooling air ingress openings and the cover plate are in a single plane, namely the plane of the cover plate itself. The air ingress openings cannot always be formed in the cover plate at the most desirable positions to direct air to those parts which need cooling the most. It is difficult to obtain proper dimensioning of the opening for the cooling air and properly dimensioned and positioned openings in relation to the elements of the alternator and of the rectifier which require cooling.